US 2017/0133194 A1 discloses a multi-beam charged particle system which uses plural electron beams in parallel for scanning an object to be inspected. The plural electron beams are generated by directing an electron beam generated by an electron source onto a multi-aperture plate having a plurality of apertures. One portion of the electrons are absorbed by the multi-aperture plate, and another portion of the electrons traverse apertures of the multi-aperture plate so that a plurality of electron beams is formed downstream of this multi-aperture plate. Moreover, one or more additional multi-aperture plates are arranged in the beam path of the electron beams downstream of the first multi-aperture plate such that each of the electron beams traverses an aperture of the additional multi-aperture plates. The additional multi-aperture plates provide electric or magnetic fields within or adjacent to their apertures in order to manipulate the electron beams traversing the apertures. For example, the electric or magnetic fields can change the convergence or the astigmatism of the beam or they can deflect the electron beam traversing an aperture.
Diameters of the apertures of the multi-aperture plates can be in the order of ten micrometers or less, and a multi-aperture plate may have more than 100 apertures. It can be challenging to produce and to handle multi-aperture plate modules including stacks of plural multi-aperture plates. A deficiency of one aperture of one multi-aperture plate of the multi-aperture plate module may result in one deficient beam such that the performance of the electron microscope is severely affected or in that the multi-aperture plate module cannot be used at all.